My pedal was really mushy, so I had a brake inspection done at Les Schwab Tires.

They replaced the MBC at 10a. The car sat all day there until 6p when I was able to pick it up. I started the car and the idle was at 1200 and I just though, oh the car is just being that way cause it sat all day in a lot.

Didn't drive it yesterday and today it idles between 1800 - 2100. And every now and then, i jumps up and down repeatedly from 1000-1500, then back to 2000 shortly after.

Any thoughts?

BTW, it my 90 LX sedan.

 

I wonder if your brake booster hose isn't hooked up properly? Check the hose that goes between the booster & the intake manifold. Otherwise I would take it back to the shop & express your concern.

 

bump, i got the same problem. help please

 

It idles that high at operating temp or before its warmed up?

 

changing the master cylinder alone should not affect idle. there is a vacuum hose to the bsoster however that MAY have been touched, but it shouldnt have.

try to track down any vacuum leak from any one of the hoses that go into the intake manifold by listening for any hissing noises. you can unplug and reconnect hoses to see if that changes anything too.

if not, then you can just try to adjust your idle back down manually. you do this by turning the idle screw on the throttle body. from the passenger side, look near the top of the throttle body, there should be a wide slotted screw. it may be covered with plastic wax too, altho im doubting that since its probably been adjusted before by now. just turn that in all the way, then back out until youre back at 750rpm.

theres a procedure in the shop manual about resetting the IACV/EACV, unplugging it, resetting the ecu.... i found its crap and simply ineffective. this is one of hte few times i go against the shop manual. just adjust the idle screw and call it done.

 

i adjusted the idle screw thing and all it would do is get higher. and its all the way to the point where the idle can no longer go lower.

 

then you have a major vacuum leak.

find it.

 

Its a vacuum leak. Either the master cylinder is no good or the hose from the manifold is bad..

 

come to think of it, theres that seal on the master cylinder against the booster wall. not sure if thats a vacuum seal or not. but maybe thats not installed properly causing the leak, if it is even a vacuum seal.

 

There is also the one way valve that is in the brake booster line. If it gets stuck open or put back on backwards it would act like a vacuum leak.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thesmogman &raquo;</TD></TR><TR><TD CLASS="quote">There is also the one way valve that is in the brake booster line. If it gets stuck open or put back on backwards it would act like a vacuum leak.</TD></TR></TABLE>

Good idea but the only problem with that is that if it was backwards , it would have blocked the air coming into the booster....

 

Not necessarily...I believe the design is that the one way closes when the vacuum in the IM drop's, Thus holding the vacuum in the booster.

So when it is turned around it would just flow. Now if it was pushing air from the IM to it, it would close.

But anyway an easy way to check it would be to unplug it from the manifold and plug the IM nipple off. Don't drive the car!! just see if the idle return's.

 

ok so there is a high chance of me having a bad master cylinder?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ef.love &raquo;</TD></TR><TR><TD CLASS="quote">ok so there is a high chance of me having a bad master cylinder?</TD></TR></TABLE>

no. who said that?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IT GUY &raquo;</TD></TR><TR><TD CLASS="quote">It idles that high at operating temp or before its warmed up?</TD></TR></TABLE>

Mine is at 1300 at start and 2100 after warming up.

I just checked it out in the day light. Sticky parts. I just need to do some cleaning. All my hoses are fine.

 

Once again another problem that's not related to the booster, you could check your intake manifold gasket. To do this get yourself a rag & some throttle body cleaner. Spray the cleaner around the IM and if the engine begins to stall then you have a leak there. (the rag is to whip the excess cleaner up) This will also help you clean up back there a little bit

 

It may just be a coincidence that the brake booster was changed at the same time this problem popped up. i would also look into the FITV and IACV.

look here
https://honda-tech.com/zerothread?id=2153910